1. Field of the Invention
The invention relates to robot arms or motion platforms and more particularly to a spherical coordinates manipulating mechanism capable of maneuvering payloads by carrying out multiple degrees-of-freedom.
2. Description of Related Art
Conventionally, gimbals type multi-ring mechanisms are used in devices involving spherical coordinates motion. Its multiple rings permit the payload it carries to rotate continuously in large angles. The mechanism having less payload capacity and inefficient inertia would have limited applications. However, it is constructed by connecting arc-links sequentially. In order to meet the output requirement, each ring must have a significantly increased diameter to contain the corresponding actuator assemblies, resulting in the overall mechanism to be excessively large and out of proportion with the payload capacity. The presence of actuator assemblies mounted to moving parts of the orientating mechanism may cause bulkiness and complexity of the mechanism. In addition, difficulty in electric connections may exist between the actuator assemblies coupled to the rings, and the inter-twisted wires may also hinder the operation of the mechanism.
In 1990, a 3-RRR spherical parallel mechanism named Agile Eye was invented by professors C. M. Gosselin and J. F. Hamel of University Lavel. When viewing the Agile Eye from above, there can be seen three concentric axes on the mechanism formed at 120° relative to one another. The mechanism consists of three rotating inputs, which actuate a series of spherical linkages to orient a payload. The Agile Eye takes advantage of parallel mechanism and can orient in three degrees-of-freedom. Another configuration, a two degrees-of-freedom version (U.S. Pat. No. 5,966,991) was also invented by Professor C. M. Gosselin. This orientating device employs a spherical five-bar linkage mechanism.